A load power train control of the general type identified above is already in use. The prior art pressure control device is formed by a pressure modulator that is connected in series to a clutch valve, a safety valve, and a manually operated changeover switch for control either of the forward or reverse shift clutch. In the changeover of the shift clutches from forward to reverse and/or during the first time control of the respective shift clutches after starting the vehicle engine, the pressure modulator causes the clutch shift pressure to be built up slowly according to a transition function before the clutch is completely engaged with full control pressure. This causes a smooth start of the vehicle, without the foot clutch having to be actuated. The safety valve functions so that, after cutting off of the engine and after renewed starting, at first neither of the shift clutches is engaged. This ensures that the vehicle is kept from moving unintentionally after starting the engine.
Since, in addition to the automatic starting process, the possibility must also be offered of shifting the vehicle by means of the foot clutch, the clutch valve is provided. By the incorporation, according to the prior art, of the clutch valve in the circuit comprising the pressure modulator, the safety valve, and the shift valve, when the clutch valve is used, the function of the pressure modulator also has an effect on the closing of the reversible shift clutches, and engagement of the shift is delayed when the clutch pedal is stepped on. As a result, a sensitive and measured engagement and thus an exact shifting of the vehicle is made more difficult for the operator.